Exhaust gas-purifying system for internal combustion engines

Abstract

An exhaust gas-purifying system for an internal combustion engine has an adsorbing device arranged in an exhaust passage thereof for adsorbing or desorbing unburnt component contained in exhaust gases. An exhaust gas recirculation passage branches off from the exhaust passage at a branch point downstream of the adsorbing device and extending to an intake passage of the engine for returning exhaust gases flowing through the adsorbing device to the intake passage. The path of exhaust gases is changed to selectively introduce the exhaust gases containing the unburnt components into the exhaust gas recirculation passage. The adsorbing capacity of the adsorbing device is checked based on a manner of change in an air-fuel ratio of exhaust gases detected when the exhaust gases are introduced into the exhaust gas recirculation passage.

What is claimed is: 
     
       1. In combination with an internal combustion engine having an intake passage, an exhaust passage, an air-fuel ratio sensor arranged in said exhaust passage, for detecting an air-fuel ratio of exhaust gases from said engine and generating an electric signal indicative of the detected air-fuel ratio of said exhaust gases, a control means for performing the function of calculating an air-fuel ratio control amount for controlling an air-fuel ratio of an air-fuel mixture supplied to said engine to a predetermined air-fuel ratio in response to said air-fuel ratio of said exhaust gases detected by said air-fuel ratio sensor, and an exhaust gas-purifying system including an adsorbing device arranged in said exhaust passage for adsorbing or desorbing said unburnt components contained in said exhaust gases, the improvement comprising:   an exhaust gas recirculation passage branching off from said exhaust passage at a first branch point downstream of said adsorbing device and extending to said intake passage, for returning exhaust gases flowing through said adsorbing device to said intake passage;   changeover means for changing a path of exhaust gases to selectively introduce said exhaust gases containing said unburnt components into said exhaust gas recirculation passage; and   said control means further performing the function of checking adsorbing capacity of said adsorbing device, based on a manner of change in said air-fuel ratio indicated by said electric signal generated by said air-fuel ratio sensor when said exhaust gases are introduced into said exhaust gas recirculation passage.   
     
     
       2. The combination according to claim 1, wherein said function of checking adsorbing capacity includes determining said manner of change in said air-fuel ratio indicated by said electric signal generated by said air-fuel ratio sensor from a manner of change in said air-fuel ratio control amount calculated when said exhaust gases are introduced into said exhaust gas recirculation passage. 
     
     
       3. The combination according to claim 1, wherein said exhaust passage has a branch passage bypassing said adsorbing device in a fashion branching off from said exhaust passage at a second branch point upstream of said adsorbing device and joining said exhaust passage at a point downstream of said first branch point, and second changeover means arranged in said exhaust passage at said second branch point, for selectively introducing said exhaust gases into said exhaust passage and said bypass passage. 
     
     
       4. The combination according to claim 1, including a temperature sensor for detecting a temperature of said adsorbing device and generating an electric signal indicative of the detected temperature of said adsorbing device, and wherein said control unit further performs the function of permitting execution of checking of said adsorbing capacity of said adsorbing device when the temperature of said adsorbing device indicated by said electric signal generated by said temperature sensor is above a predetermine value. 
     
     
       5. The combination according to claim 3, including a temperature sensor for detecting a temperature of said adsorbing device, and wherein said control unit further performs the function of permitting execution of checking of said adsorbing capacity of said absorbing device means, when the temperature of said adsorbing device indicated by said electric signal generated by said temperature sensor is above a predetermined value. 
     
     
       6. The combination according to claim 1, wherein said function of checking adsorbing capacity includes determining that there is abnormality in said function of checking adsorbing capacity adsorbing device when a time period over which said air-fuel ratio control amount is below a predetermined value is shorter than a predetermined time period. 
     
     
       7. The combination according to claim 3, wherein said function of checking adsorbing capacity includes determining that there is abnormality in said adsorbing device when a time period over which said air-fuel ratio control amount calculated by said calculating means is below a predetermined value is shorter than a predetermined time period. 
     
     
       8. The combination according to claim 4, wherein said function of checking adsorbing capacity includes abnormality determining that there is abnormality in said adsorbing device when a time period over which said air-fuel ratio control amount calculated by said calculating means is below a predetermined value is shorter than a predetermined time period. 
     
     
       9. The combination according to claim 5, wherein said function of checking adsorbing capacity includes determining that there is abnormality in said adsorbing device when a time period over which said air-fuel ratio control amount calculated by said calculating means is below a predetermined value is shorter than a predetermined time period. 
     
     
       10. The combination according to claim 1, wherein said control unit further performs the functions of calculating a difference between said air-fuel ratio control amount and a predetermined reference value, and determining that there is abnormality in said adsorbing device when a cumulative value of said difference over a predetermined time period is below a predetermined value. 
     
     
       11. The combination according to claim 3, wherein said control unit further performs the functions of calculating a difference between said air-fuel ratio control amount and a predetermined reference value, and determining that there is abnormality in said adsorbing device when a cumulative value of said difference over a predetermined time period is below a predetermined value. 
     
     
       12. The combination according to claim 4, wherein said control unit further performs the functions of calculating a difference between said air-fuel ratio control amount means and a predetermined reference value, and determining that there is abnormality in said adsorbing device when a cumulative value of said difference over a predetermined time period is below a predetermined value. 
     
     
       13. The combination according to claim 5, wherein said control unit further performs the functions of calculating a difference between said air-fuel ratio control amount and a predetermined reference value, and determining that there is abnormality in said adsorbing device when a cumulative value of said difference over a predetermined time period is below a predetermined value.